Vegetable protein products obtained from seed and leaf materials are used as replacements and extenders for proteins derived from animal, marine and poultry sources. Such vegetable protein products are usually low fat or defatted materials. They are commonly referred to as "flours" if they contain less than 65% protein, as "concentrates" if they contain from 65 to 90% protein and as "isolates" if they contain above 90% protein. Some methods for manufacturing vegetable protein products customarily include heat treatment and aqueous alcohol extraction, as well as other chemical treatments and applied conditions which denature and substantially reduce the functional properties of the proteinaceous products. These functional properties of such proteins are characterized by their ability to hold oil or fat and water, to emulsify and to form protein-containing products having a firm consistency.
Since these functional properties of the protein in a vegetable protein product are desired characteristics in many applications, as for example in food recipes (e.g. in meat, dairy and bakery products) and in industrial applications (e.g. in the paper coating industry), the enhancing of these properties in low functional proteinaceous materials is thus of substantial economic and technological importance.
Although one of the functional properties of protein is its solubility, the other properties are not necessarily interdependent on the protein solubility and soluble protein material can have other poor functional properties, while protein material of low solubility can have high functional properties. It is well known that protein material which is normally soluble at pH's other than its isoelectric pH, has a reduced solubility in all pH ranges when it becomes denatured and will not be affected by either simple alkaline or acid treatments which will only change the pH. Likewise, upon denaturing, most of the original functional properties, as hereinbefore stated, will be lost.
Prior art teachings indicate that in order to introduce or regenerate some of these functional properties in denatured material, either, high temperatures above the boiling point of water, such as are obtained by steam jet cookers, or high shear forces, as obtained by successive pressure and cavitation cycling, such for example, by using a centrifugal homogenizer, must be employed on an aqueous, slightly alkaline slurry of the denatured proteinaceous material.
A patent by Gobi et al, (U.S. Pat. No. 4,113,716) discloses a process designed to obtain improved soy protein fractions from previously denatured soy protein material by cooking slightly alkaline aqueous slurry of the denatured soy protein material at temperatures between 110.degree. C. to 150.degree. in a jet cooker chamber and obtaining from this high temperature treated material soluble fractions with "properties superior to those obtained by using undenatured defatted soy flakes as starting material."
A patent by Howard et al (U.S. Pat. No. 4,234,620) discloses a process in which aqueous vegetable protein dispersions are subjected to high shear forces of successive pressure and cavitation cycling obtained by centrifugal homogenization at temperatures below 150.degree. C., under slight alkaline pH's, to provide a high protein solubility, low viscosity product at high solids levels, which may be dried, generally after pH adjustment with acid, to provide a vegetable protein product similar to milk protein.
British Patent No. 1,575,052 discloses that the flavor, color, nutritive value and some functional properties of protein material selected from single cell protein material, plant protein material, whey solids and mixtures thereof can be improved by heating aqueous slurries of the protein material to temperatures ranging from 75.degree. to 100.degree. C., adjusting the pH to a pH range of 6.6 to 8, preferably 7.2 to 7.6, by adding a pH adjusting compound, preferably a calcium compound, maintaining the temperature for a period of 1-120 minutes and drying the product. The product obtained may be used as a replacer for egg solids and non-fat dry milk, especially in baked goods, as the process reduces the yeasty off-flavor, releases buffering materials from yeast cell material, saponifies lipid material and reduces available thiol (-SH) groups.
The present invention is based on a surprising discovery that some of the functional properties of denatured protein in a vegetable protein product can be enhanced, without causing substantial changes in the protein by a very simple, economical and efficient process. The enhanced properties include the ability to hold oil or fat and water, to emulsify and to form products of firm consistency. The process of the present invention does not require the use of temperatures above 100.degree. C., nor any special equipment or forces. As will be seen from the details described below, the process of the invention provides a simple low-cost vegetable protein product having improved functional properties compared with corresponding untreated denatured proteinaceous material.
It is the object of the present invention to enhance the functional properties of denatured vegetable proteinaceous material having poor functional properties.
Another object of the invention is to enhance the functional properties of denatured vegetable proteinaceous material without fractionation, without addition or introduction of salts, without super-heating above water boiling temperature, and without the use of high shear forces such as obtained by centrifugal homogenization.
Yet another object of the invention is to provide a simple, efficient and economical process to achieve the same.
A further object of the invention is to provide a vegetable proteinaceous material having enhanced functional properties.